Third generation partnership project (3GPP) mobile communication systems based on a wideband code division multiple access (WCDMA) radio access technology are widely spread all over the world. High-speed downlink packet access (HSDPA) that can be defined as a first evolutionary stage of WCDMA provides 3GPP with a radio access technique that is highly competitive in the mid-term future. However, since requirements and expectations of users and service providers are continuously increased and developments of competing radio access techniques are continuously in progress, new technical evolutions in 3GPP are required to secure competitiveness in the future.
An orthogonal frequency division multiplexing (OFDM) system capable of reducing inter-symbol interference with a low complexity is taken into consideration as one of next generation (after 3G) systems. In the OFDM system, serial input data symbols are converted into N parallel data symbols and are carried and transmitted on separate N subcarriers. The subcarriers maintain orthogonality in a frequency dimension. Orthogonal frequency division multiple access (OFDMA) is a multiple access scheme in which multiple access is achieved by independently providing some of available subcarriers to a plurality of users in a system using the OFDM as a modulation scheme.
One of primary problems of the OFDM/OFDMA system is that a peak-to-average power ratio (PAPR) can be significantly large. The PAPR problem is that a peak amplitude of a transmit (Tx) signal is significantly larger than an average amplitude. This is caused by the fact that OFDM symbols are N sinusoidal signals overlapping on different subcarriers. In particular, since the PAPR is related to battery capacity, the PAPR is problematic when a user equipment (UE) is sensitive to power consumption. The PAPR needs to be reduced to decrease power consumption.
A single carrier-frequency division multiple access (SC-FDMA) system is one of systems proposed to reduce the PAPR. An SC-FDMA is a combination of a single carrier-frequency division equalization (SC-FDE) and a frequency division multiple access (FDMA). The SC-FDMA has a similar characteristic with an OFDMA in that data is modulated and demodulated in a time domain and a frequency domain by using a discrete Fourier transform (DFT). However, the SC-FDMA is advantageous over the OFDMA in terms of Tx power saving due to a low PAPR of a Tx signal. In particular, regarding the use of batteries, the SC-FDMA is advantageous in uplink communication in which communication is made to a base station (BS) from a UE sensitive to Tx power.
A wide coverage is important when the UE transmits data to the BS. Although a bandwidth of Tx data is small, power can be concentrated in the wide coverage. The SC-FDMA system provides a signal with little variation, and thus has a wider coverage than other systems when the same power amplifier is used.
In order to implement various transmission or reception methods to achieve high-speed packet transmission, transmission of a control signal on time, spatial, and frequency domains is an essential and indispensable factor. A channel for transmitting the control signal is referred to as a control channel. An uplink control signal may be various such as an acknowledgement (ACK)/negative-acknowledgement (NACK) signal which is a response for downlink data transmission, a channel quality indicator (CQI) indicating downlink channel quality, a precoding matrix index (PMI), a rank indicator (RI), etc.
One example of the control signal is a scheduling request. The scheduling request is used when a UE requests a BS to allocate an uplink radio resource. The scheduling request is a sort of preliminary information exchange for exchanging uplink data. The UE first transmits the scheduling request and is allocated with an uplink radio resource. Thereafter, the UE transmits uplink data to the BS. When in an idle mode, the UE can transmit an uplink radio resource allocation request through a conventional random access process. However, when in a connected mode, a service may be delayed if the UE transmits the uplink radio resource allocation request through the conventional random access process. This is because the random access is a contention based process, and thus allocation of the uplink radio resource can be delayed. Therefore, when in the connected mode, the scheduling request may be transmitted through a control channel in order to provide effective resource allocation in a more reliable and rapid manner.
Compatibility with another control channel for transmitting another control signal has to be taken into consideration when the scheduling request needs to be transmitted on an uplink control channel. In addition, capacity of the control channel for transmitting the scheduling request has to be also taken into consideration.
Accordingly, there is a need for a control channel having an effective structure for transmitting a scheduling request.